In the manufacture of gas turbine engine components, such as gas turbine engine blades and vanes, an appropriate alloy, such as a nickel or cobalt based superalloy, is investment cast in a ceramic investment mold. One or more ceramic cores may be present in the ceramic investment mold in the event the cast component is to include one or more internal passages. For example, gas turbine blades and vanes for modern, high performance gas turbine engines typically include internal cooling passages extending through the airfoil and root portions and through which passages compressor bleed air is conducted to cool the airfoil portion during engine operation. In this event, the ceramic core positioned in the investment mold will have a configuration corresponding to the internal cooling passage(s) to be formed through the airfoil and root portions of the cast turbine blade or vane. The blade or vane component may be cast by well known techniques to have an equiaxed, columnar, or single crystal microstructure.
In the past, the ceramic core has been removed from the investment cast component by an autoclave technique or an open kettle technique. One autoclave technique involves immersing the cast component in an aqueous caustic solution (e.g. 45% KOH) at elevated pressure and temperature (e.g. 250 psi and 177.degree. C. ) for an appropriate time (e.g. 4-10 hour cycles) to dissolve the core from the casting. U.S. Pat. Nos. 4,134,777 and 4,141,781 disclose autoclave caustic leaching of yttria ceramic cores and beta alumina ceramic cores from directionally solidified superalloy castings. An exemplary open kettle technique involves immersing the cast component in a similar aqueous caustic solution at ambient pressure and elevated temperature (e.g. 132.degree. C.) with agitation of the solution for a time (e.g. 90 hours) to dissolve the core from the casting. These core removal techniques are quite slow and time-consuming.